Je ne parle pas Francais bien, mais je vais essayer de répondre par Anglais.
If I translated your question correctly you ask how I was able to have both an 8 speed gearbox and a reverse gear, right? The answer is that I have a D-N-R switch in the center console. If that is switched to R a separate driveline is engaged that only contains the reverse gear. If it is switched to D it uses the driveline that goes through the 8-speed gearbox.